Wireless power feeding system and wireless power feeding method

ABSTRACT

An object is to provide a power feeding system and a power feeding method which are more convenient for a power feeding user at the power receiving end. An object is to provide a power feeding system and a power feeding method which also allow a power feeding provider (a company) which feeds power (at the power transmitting end) to supply power without waste. A power feeding device which wirelessly supplies power to a power receiver detects the position and the resonant frequency of the power receiver to be supplied with power, and controls the frequency of a power signal to be transmitted to the power receiver on the basis of the information. An efficient power feeding service can be offered by transmitting a power signal to the power receiver at an optimum frequency for high power transmission efficiency.

TECHNICAL FIELD

The present invention relates to a wireless power feeding system and awireless power feeding method.

BACKGROUND ART

In recent years, electronic devices using electric power as a drivingpower, as typified by mobile devices such as mobile phones or notebookpersonal computers, are often used while being carried.

In addition, transportation means such as bicycles and automobiles whichuse electric power as a driving power have been developed in terms ofits cleanness and safety in the aspect of environment.

It is difficult to supply power to such electronic devices andtransportation means, which are used outdoors or while in motion,constantly from a commercial power supply distributed to each house,through wires. Therefore, portable electronic devices and transportationmeans incorporate batteries which are charged from a commercial powersupply in advance and operate by being supplied with power from thebatteries.

Thus, the operating time of electronic devices is limited by the amountof power stored in the battery. In order to use the electronic devicecontinuously for a long time, a user needs to prepare a spare battery,or to find a commercial power supply from which the battery can berecharged near his destination.

Therefore, a contactless power feeding system has been proposed and amore efficient power feeding system in view of a problem with anobstacle and the like has been studied so that the battery can be fedwith power even if there is no commercial power supply (see, e.g.,Patent Document 1).

REFERENCE

[Patent Document 1] Japanese Published Patent Application No.2010-119246

DISCLOSURE OF INVENTION

However, a contactless power feeding system has a problem in that it hasdifficulty specifying or managing a power feeding user who receivespower (at the power receiving end), controlling the amount of powersupplied to a power receiver, and the like because it is a contactlesssystem.

Therefore, it is an object to provide a power feeding system and a powerfeeding method which are more convenient for a power feeding user at thepower receiving end.

It is an object to provide a power feeding system and a power feedingmethod which also allow a power feeding provider (a company) which feedspower (at the power transmitting end) to supply power to a powerreceiver without waste.

It is an object to provide a power feeding system and a power feedingmethod which can offer a power feeding service efficient to both a userand a provider by specifying and managing a power feeding user at thepower receiving end and properly controlling the amount of powersupplied to a power receiver.

A power feeding device detects a resonant frequency which is specific toa power receiver and controls the frequency of a power signal to betransmitted to the power receiver on the basis of the information on theresonant frequency.

The power feeding device can also identify and manage a power receiverby receiving identification information of the power receiver.

One example of wireless power feeding is a power feeding method using anantenna. With a certain antenna shape, the efficiency of transmission ofpower fed from a power feeding device to a power receiver depends on thefrequency of a power signal to be transmitted, the distance between thepower feeding device and the power receiver, the resonant frequencyspecific to the power receiver, or the like.

Note that in this specification, a distance between a power feedingdevice and a power receiver is the shortest distance between an antennaprovided in the power feeding device and an antenna of the powerreceiver.

If the frequency of a power signal to be transmitted is fixed to a givenvalue f₀, the efficiency of transmission of power fed from the powerfeeding device to the power receiver reaches the maximum value when thedistance between the power feeding device and the power receiver isd_(MAX(0)).

The distance d_(MAX) with which the efficiency of transmission of powerfed from the power feeding device to the power receiver reaches themaximum value varies with the frequency f of the power signal to betransmitted and is specific to the frequency f of each power signal.

Thus, if the distance between the power feeding device and the powerreceiver is fixed to a given value d₀, it is possible to determine thefrequency f_(MAX(0)) of a power signal to be transmitted, at which theefficiency of transmission of power fed from the power feeding device tothe power receiver reaches the maximum value.

In this specification, a resonant frequency is defined as f_(MAX(a)) atwhich power transmission efficiency reaches the maximum value, with adistance d_(a) between the power feeding device and the power receiver.

If power transmitted from a power feeding device is P_(a) and powerreceived by a power receiving device is P_(b), the ideal powertransmission efficiency is P_(b)/P_(a)×100. P_(b) is ideallyproportional to V_(b) ²/R_(b) where R_(b) is the load of the powerreceiving device and V_(b) is the voltage amplitude of a signal receivedby the power receiving device. Furthermore, P_(a) is ideallyproportional to V_(a) ²/R_(a) where R_(a) the load of the power feedingdevice and V_(a) is the voltage amplitude of a signal transmitted fromthe power feeding device. Thus, the power transmission efficiencyP_(b)/P_(a)×100 is proportional to V_(b) ²×R_(a)/V_(a) ²×R_(b). The loadR_(a) of the power feeding device and the load R_(b) of the powerreceiving device are usually fixed; thus, the power transmissionefficiency increases as V_(b) increases. In addition, the powertransmission efficiency peaks when V_(b) peaks. Since the frequency atwhich power transmission efficiency peaks is defined as f_(max) in thisspecification as described above, V_(b) peaks at that frequency.

In a wireless power feeding method disclosed in this specification, apower feeding device receives a plurality of signals having differentfrequencies which are transmitted from a power receiver. Then, the powerfeeding device detects the intensities of the received signals havingdifferent frequencies and determines a frequency corresponding to a highintensity signal.

Here, a frequency corresponding to a high intensity signal can bereferred to as a frequency corresponding to a signal of large voltageamplitude. In other words, a frequency corresponding to the signal ofthe highest intensity corresponds to the received signal of the largestvoltage amplitude, and that frequency is a resonant frequency.

Note that the power feeding device determines the intensities of theplurality of received signals having different frequencies and, inaddition, can find out the position of the power receiver from thefrequencies and intensities. The position of the power receiver can alsobe referred to as the distance between the power feeding device and thepower receiver.

After finding out the resonant frequency, the power feeding devicetransmits a power signal at that resonant frequency to the powerreceiver.

The power feeding device can supply power to the power receiver withoutwaste by transmitting a power signal to the power receiver at an optimumfrequency for high power transmission efficiency.

The power receiver and the power feeding device each have atransmission/reception circuit portion which transmits and receiveselectromagnetic waves to and from the other and a signal processingcircuit portion which processes electrical signals of theelectromagnetic waves to be transmitted and received. The signalprocessing circuit portion of the power receiver has a power receptioncontrol function to control power to be received from the power feedingdevice. The signal processing circuit portion of the power feedingdevice has a position and resonant frequency detection function to findout the distance between the power feeding device and the power receiverand the resonant frequency, and a power transmission control function tocontrol power to be transmitted to the power receiver.

The power receiver includes a power receiving device portion and a powerload portion and can operate the power load portion using power storedin a power storage portion of the power receiving device portion. Inthis specification, a power receiver means an object which operatesusing received electric power as a driving power, and examples of thepower receiver include portable electronic devices such as mobilephones, transportation means driven by an electric motor (automobiles,motorized bicycles, aircrafts, ships, and railroad cars), and the like.

One embodiment of a power feeding system disclosed in this specificationincludes a power feeding device and a power receiver including a powerreceiving device portion. The power feeding device includes atransmission/reception circuit portion which transmits and receives anelectromagnetic wave, a signal processing circuit portion whichprocesses an electrical signal of the electromagnetic wave to betransmitted and received by the transmission/reception circuit portion,and a power supply portion which supplies power to be transmitted to thepower receiver. The signal processing circuit portion of the powerfeeding device has a position and resonant frequency detection functionto detect the position and the resonant frequency of the power receiverand a power transmission control function to control power to betransmitted to the power receiver. The power receiving device portionincludes a transmission/reception circuit portion which transmits andreceives an electromagnetic wave, a signal processing circuit portionwhich processes an electrical signal of the electromagnetic wave to betransmitted and received by the transmission/reception circuit portion,and a power storage portion including a secondary battery which storespower transmitted from the power feeding device and supplies power to beconsumed by a power load portion. The transmission/reception circuitportion of the power receiving device portion has a power receptioncontrol function to control power to be received from the power feedingdevice.

Another embodiment of a power feeding system disclosed in thisspecification includes a power feeding device and a power receiverincluding a power receiving device portion. The power feeding deviceincludes a transmission/reception circuit portion which transmits andreceives an electromagnetic wave, a signal processing circuit portionwhich processes an electrical signal of the electromagnetic wave to betransmitted and received by the transmission/reception circuit portion,and a power supply portion which supplies power to be transmitted to thepower receiver. The signal processing circuit portion of the powerfeeding device has a position and resonant frequency detection functionto detect the position and the resonant frequency of the power receiverand a power transmission control function to control power to betransmitted to the power receiver. The power receiving device portionincludes a transmission/reception circuit portion which transmits andreceives an electromagnetic wave, a signal processing circuit portionwhich processes an electrical signal of the electromagnetic wave to betransmitted and received by the transmission/reception circuit portion,a power storage portion including a secondary battery which stores powertransmitted from the power feeding device and supplies power to beconsumed by a power load portion, and a detection portion which detectsthe voltage, the current, or the voltage and current outputted from thesecondary battery. The transmission/reception circuit portion of thepower receiving device portion has a power reception control function tocontrol power to be received from the power feeding device.

In each of the above embodiments, the transmission/reception circuitportion of the power feeding device and the transmission/receptioncircuit portion of the power receiving device portion can each includean antenna circuit, a rectifier circuit, a modulation circuit, ademodulation circuit, an oscillator circuit, and a power supply circuit.

In each of the above embodiments, the power receiver may include amemory portion which stores identification information to be read by thesignal processing circuit portion of the power receiving device portion,and the signal processing circuit portion of the power feeding devicemay have an identification function to identify the identificationinformation.

One embodiment of a power feeding method disclosed in this embodimentincludes a first step of transmitting a position and resonant frequencydetection signal from a power receiver to a power feeding device anddetecting the position and the resonant frequency of the power receiverwith the power feeding device, a second step of adjusting the frequencyof a power signal to be transmitted from the power feeding device on thebasis of the position and the resonant frequency of the power receiverand transmitting power from the power feeding device to the powerreceiver, and a third step of storing the power transmitted from thepower feeding device in a secondary battery of a power storage portionof the power receiver.

The power receiver can transmit a plurality of signals having differentfrequencies as a position and resonant frequency detection signal, andthe power feeding device can detect the position and the resonantfrequency of the power receiver by receiving the plurality of signalshaving different frequencies and detecting the intensities of theplurality of signals having different frequencies.

The power receiver may detect the voltage, the current, or the voltageand current outputted from the secondary battery and transmit a powerfeeding request signal or a power reception end signal to the powerfeeding device according to the detection information.

In the above embodiment, a step of recognizing identificationinformation of the power receiver with the power feeding device may beperformed before the first step of detecting the position and theresonant frequency of the power receiver.

In power feeding performed by the power feeding device and the powerreceiver, a power signal is transmitted to the power receiver at anoptimum frequency for high power transmission efficiency on the basis ofthe position and the resonant frequency information of the powerreceiver; accordingly, power can be supplied to the power receiverwithout waste.

Therefore, it is possible to provide a power feeding system and a powerfeeding method which are more convenient for a power feeding user.

It is possible to provide a power feeding system and a power feedingmethod which also allow a power feeding provider (a company) which feedspower (at the power transmitting end) to supply power to a powerreceiver without waste.

It is possible to provide a power feeding system and a power feedingmethod which can offer a power feeding service efficient to both a userand a provider by specifying and managing a power feeding user at thepower receiving end and properly controlling the amount of powersupplied to a power receiver.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 2 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 3 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 4 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 5 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 6 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 7 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIGS. 8A and 8B each illustrate an embodiment of a wireless powerfeeding system and a wireless power feeding method.

FIG. 9 illustrates an embodiment of a wireless power feeding system anda wireless power feeding method.

FIG. 10 illustrates an embodiment of a power receiver.

FIG. 11 illustrates the relationship between power transmission distanceand power transmission efficiency.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail belowwith reference to the drawings. Note that the present invention is notlimited to the description below, and it is easily understood by thoseskilled in the art that modes and details disclosed herein can bemodified in various ways. In addition, the present invention should notbe construed as being limited to the description in the embodimentsgiven below.

Note that ordinal numbers such as “first”, “second”, and “third” areused for convenience and do not denote the order of steps or thestacking order of layers. In addition, the ordinal numbers in thisspecification do not denote any particular names to define theinvention.

Embodiment 1

In this embodiment, an embodiment of a wireless power feeding system anda wireless power feeding method is described with reference to FIGS. 1to 4.

FIG. 2 and FIG. 3 illustrate components of a power feeding device and apower receiver included in the wireless power feeding system of thisembodiment, in independent blocks which are classified according totheir functions. However, there is not necessarily a one-to-onecorrespondence between components and functions, and the power feedingsystem may operate using a plurality of components and a plurality offunctions in conjunction with each other.

In the wireless power feeding system in FIG. 2, a power feeding device20 and a power receiver 10 transmit and receive signals to and from eachother wirelessly (by an electromagnetic wave), and power is suppliedfrom the power feeding device 20 to the power receiver 10 withoutcontact.

The power feeding device 20 includes a transmission/reception circuitportion 210 which transmits and receives electromagnetic waves, a signalprocessing circuit portion 220 which processes electrical signals of theelectromagnetic waves to be transmitted and received, and a power supplyportion 230 which supplies power to be transmitted to the power receiver10.

Note that FIG. 3 illustrates a more detailed specific example of thetransmission/reception circuit portion 210. In FIG. 3, thetransmission/reception circuit portion 210 includes an antenna circuit211, a rectifier circuit 212, a modulation circuit 213, a demodulationcircuit 214, an oscillator circuit 215, and a power supply circuit 216.

An electromagnetic wave (a signal) received by the antenna circuit 211is converted into an electrical signal by the antenna circuit 211 andrectified in the rectifier circuit 212. The rectified signal isdemodulated in the demodulation circuit 214 and then transmitted to thesignal processing circuit portion 220. On the other hand, a transmissionsignal generated in the signal processing circuit portion 220 istransmitted from the antenna circuit 211 to the power receiver 10 as anelectromagnetic wave (a signal) when voltage is applied to the antennacircuit 211 by the modulation circuit 213 in response to a signal with acertain frequency generated in the power supply circuit 216 and theoscillator circuit 215. Note that the frequency of a signal transmittedfrom the oscillator circuit 215 is adjusted by the power supply circuit216.

In the case where the transmission signal is a power signal for powertransmission, the signal processing circuit portion 220 receives powerfrom the power supply portion 230. The power supply portion 230 isconnected to a power supply network or a power generation system inorder to supply power to the power receiver 10.

The power receiver 10 includes a power receiving device portion 100 anda power load portion 150. The power receiving device portion 100includes a transmission/reception circuit portion 110 which transmitsand receives electromagnetic waves, a signal processing circuit portion120 which processes electrical signals of the electromagnetic waves tobe transmitted and received, a memory portion 140, and a power storageportion 130 including a secondary battery 131 which stores powertransmitted from the power feeding device 20. Note that the memoryportion 140 may be provided as needed, and the memory portion 140 canstore identification information of the power receiver 10 and the like.

Note that FIG. 3 illustrates a more detailed specific example of thetransmission/reception circuit portion 110. In FIG. 3, thetransmission/reception circuit portion 110 includes an antenna circuit111, a rectifier circuit 112, a modulation circuit 113, a demodulationcircuit 114, an oscillator circuit 115, and a power supply circuit 116.

An electromagnetic wave (a signal) received by the antenna circuit 111is converted into an electrical signal by the antenna circuit 111 andrectified in the rectifier circuit 112. The rectified signal isdemodulated in the demodulation circuit 114 and then transmitted to thesignal processing circuit portion 120. On the other hand, a transmissionsignal generated in the signal processing circuit portion 120 istransmitted from the antenna circuit 111 to the power feeding device 20as an electromagnetic wave (a signal) when voltage is applied to theantenna circuit 111 by the modulation circuit 113 in response to asignal with a certain frequency generated in the oscillator circuit 115.Note that the frequency of a signal transmitted from the oscillatorcircuit 115 is adjusted by the power supply circuit 116.

In the case where the received electromagnetic wave is anelectromagnetic wave for power reception, it is converted into anelectrical signal by the antenna circuit 111, rectified in the rectifiercircuit 112, and then stored as power (electrical energy) in thesecondary battery 131 of the power storage portion 130 via the signalprocessing circuit portion 120.

The secondary battery 131 is a power storage means. For example, alead-acid battery, a nickel-cadmium battery, a nickel-hydride battery, alithium-ion battery, or the like can be used.

Note that in the block diagrams in FIG. 2 and FIG. 3, a DC-DC convertercan be provided as appropriate. In addition, in the power storageportion 130, a power supply circuit or an overcharge control circuit forcontrolling operation of the power supply circuit so as to preventovercharging of the secondary battery 131 may be provided asappropriate, and the power supply circuit can supply power (electricalenergy) stored in the secondary battery 131 to the power load portion150 as a constant voltage.

As a modulation method used by the modulation circuit 113 or themodulation circuit 213, any of a variety of methods such as amplitudemodulation, frequency modulation, and phase modulation can be employed.

The power storage portion 130 may include a discharge control circuit.The discharge control circuit has a function to control the supply ofpower or the amount of power to be supplied to the power load portion150. The discharge control circuit makes it possible to supply power asneeded or adjust the amount of power to be supplied.

Although not illustrated in FIG. 2 and FIG. 3 (and FIG. 6), the powerreceiving device portion 100 includes a power supply circuit and acapacitor for generating power to be supplied to the power receivingdevice portion 100. In the transmission/reception circuit portion 110,power is generated from the signal received by the antenna circuit 111.The rectifier circuit is used for the generation of power. The generatedpower is supplied to the transmission/reception circuit portion 110, thesignal processing circuit portion 120, and the memory portion 140. Notethat in the case where power is stored in the secondary battery 131 ofthe power storage portion 130, power may be supplied from the secondarybattery 131 to the transmission/reception circuit portion 110, thesignal processing circuit portion 120, the memory portion 140, and thelike. In the case of the configuration where power is supplied from thesecondary battery 131, the power supply circuit and the capacitor forgenerating power to be supplied to the power receiving device portion100 are not necessarily provided.

The signal processing circuit portion 220 of the power feeding device 20has a position and resonant frequency detection function 223 to detectthe distance to the power receiver 10 and the resonant frequency of thepower receiver 10, and a power transmission control function 222 tocontrol power to be transmitted to the power receiver 10.

On the other hand, the signal processing circuit portion 120 of thepower receiver 10 has a power reception control function 122 to controlpower to be received from the power feeding device 20.

The power feeding device 20 which wirelessly supplies power to the powerreceiver 10 detects the position and the resonant frequency of the powerreceiver 10 to be supplied with power and controls the frequency of apower signal to be transmitted to the power receiver 10 on the basis ofthe information.

Note that in this specification, the distance between the power feedingdevice 20 and the power receiver 10 is the shortest distance between anantenna provided in the power feeding device 20 and an antenna of thepower receiver 10. FIG. 4 illustrates an example of power feeding with adistance d between a power receiver antenna 117 provided in the powerreceiver 10 and a power feeding device antenna 217 provided in the powerfeeding device 20. In FIG. 4, the power receiver antenna 117 and thepower feeding device antenna 217 are disposed at a distance d from eachother, and power feeding is performed by generating a magnetic field300. FIG. 4 illustrates an example of power feeding by anelectromagnetic induction method using coil antennas as the antennas,and illustrates one embodiment of the shape of antennas and the methodfor transmitting electromagnetic waves which can be employed in theinvention disclosed in this specification.

In this specification, there is no particular limitation on thefrequency of a power feeding electromagnetic wave and the frequency maybe in any frequency band as long as power can be transmitted. Forexample, the frequency of a power feeding electromagnetic wave may be inany of an LF band of 135 kHz (long wave), an HF band of 13.56 MHz, a UHFband of 900 MHz to 1 GHz, and a microwave band of 2.45 GHz.

In this specification, the frequency of electromagnetic waves used as avariety of signals (such as an electrical signal transmittingidentification information and the like and a position and resonantfrequency detection signal) may be in the same frequency band as a powerfeeding electromagnetic wave or may be in a different frequency band.Note that in the case of using frequencies in different frequency bands,separate antennas for the frequencies are preferably provided.

In this specification, the method of transmitting electromagnetic wavesmay be appropriately selected from a variety of methods such as anelectric field coupling method, an electromagnetic induction method, aresonance method, and a microwave method. In order to prevent energyloss due to foreign substances containing moisture, such as rain andmud, the electromagnetic induction method or the resonance method usinga low frequency band, specifically, frequencies of a short wave of 3 MHzto 30 MHz, a medium wave of 300 kHz to 3 MHz, a long wave of 30 kHz to300 kHz, or an ultralong wave of 3 kHz to 30 kHz, is preferably used.

One example of wireless power feeding is a power feeding method using anantenna. With a certain antenna shape, the efficiency of transmission ofpower fed from the power feeding device 20 to the power receiver 10depends on the frequency of a power signal to be transmitted, thedistance between the power feeding device 20 and the power receiver 10,the resonant frequency specific to the power receiver 10, or the like.

If the frequency of a power signal to be transmitted is fixed to a givenvalue f₀, the efficiency of transmission of power fed from the powerfeeding device to the power receiver reaches the maximum value when thedistance between the power feeding device and the power receiver isd_(MAX(0)).

The distance d_(MAX) with which the efficiency of transmission of powerfed from the power feeding device to the power receiver reaches themaximum value varies with the frequency f of the power signal to betransmitted and is specific to the frequency f of each power signal.

FIG. 11 shows results of an experiment in which two antennas having anidentical shape were disposed to face each other as illustrated in FIG.4, and a signal having a frequency f with a voltage amplitude V_(a) wastransmitted from one of the antennas and the voltage amplitude V_(b)received by the other antenna was measured, at varying frequencies ofthe signal transmitted from one antenna and with varying transmissiondistances d between the two antennas having an identical shape.Specifically, the experiment was conducted under different conditions atfrequencies f of 12.06 MHz, 12.56 MHz, 13.06 MHz, 13.36 MHz, 13.56 MHz,13.86 MHz, 14.06 MHz, and 14.56 MHz and with transmission distances d of10 mm, 20 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm, 100 mm, 105 mm, 110 mm, 120 mm,130 mm, 140 mm, and 150 mm. The antennas used for the experiment arecoil antennas, which each have a size of 72 mm×42 mm, 4 loops, a linewidth of 0.5 mm, a line interval of 0.5 mm, an inductance of about 2.6μH, a parasitic capacitance of about 4 pF, and a resistance of about 1Ω.Note that the transmission efficiency in FIG. 11 is V_(b)/V_(a) where asignal with a voltage amplitude V_(a) is output from one of the antennasand received by the other antenna and a voltage V_(b) is generatedbetween two terminals of the other antenna.

As shown in FIG. 11, at any of the frequencies f, the transmissionefficiency changes so as to reach the maximum value with a certaintransmission distance (e.g., at a frequency of 13.56 MHz, thetransmission efficiency reaches the maximum value with a transmissiondistance of about 80 mm). However, the change in transmission efficiencywith respect to transmission distance, including the value of thetransmission distance with which the transmission efficiency reaches themaximum value, differs among the frequencies f Even when thetransmission distance is the same, the transmission efficiency differsamong the frequencies f.

Therefore, if the distance between the power feeding device 20 and thepower receiver 10 is fixed to a given value d₀, it is possible todetermine the frequency f_(MAX(0)) of a power signal to be transmitted,at which the efficiency of transmission of power fed from the powerfeeding device 20 to the power receiver 10 reaches the maximum value.

Power can be supplied to the power receiver without waste bytransmitting a power signal to the power receiver at an optimumfrequency for high power transmission efficiency.

An embodiment of a wireless power feeding method is described withreference to a flow chart of FIG. 1. Note that a power feeding device Kcorresponds to the power feeding device 20 in FIG. 2 and FIG. 3 and apower receiver J corresponds to the power receiver 10 in FIG. 2 and FIG.3.

First, the power receiver J transmits a position and resonant frequencydetection signal to the power feeding device K (JB1: Transmission ofposition and resonant frequency detection signal). As the position andresonant frequency detection signal, a plurality of signals havingdifferent frequencies can be used. The power feeding device K receivesthe position and resonant frequency detection signal of the powerreceiver J (KB1: Reception of position and resonant frequency dedectionsignal), and detects the position and the resonant frequency of thepower receiver J with the intensities and times of the plurality ofreceived electrical signals having different frequencies (KB2: Detectionof position and resonant frequency) (B: Position and resonant frequencydetection step). By finding out the positional relationship between thepower feeding device K and the power receiver J, the distance betweenthe power feeding device K and the power receiver J can be detected.

The power feeding device K may store information used for the detection(such as the relationship between transmission efficiency and atransmission distance at a resonant frequency as shown in FIG. 11) in amemory portion of the power feeding device K in advance. Alternatively,at the time of detection, the power feeding device K may communicatewith another management server or the like and perform detection on thebasis of information obtained from the server.

Alternatively, communication between the power feeding device K and thepower receiver J may be started from the power feeding device K. Forexample, communication may be started by transmission of a signal forinquiring about the position and resonant frequency information of thepower receiver J from the power feeding device K.

The power feeding device K adjusts the frequency of a power signal to betransmitted, on the basis of the distance to the power receiver J andthe resonant frequency of the power receiver J, so as to obtain themaximum power transmission efficiency (KC1: Adjustment of powertransmission frequency). Power can be supplied to the power receiverwithout waste by transmitting a power signal to the power receiver at anoptimum frequency for high power transmission efficiency. As a result,power feeding which is efficient and convenient for both the powerfeeding device K and the power receiver J can be performed.

The power feeding device K transmits a power transmission start signalto the power receiver J (KC2: Transmission of power transmission startsignal), and the power receiver J receives the power transmission startsignal (JD1: Reception of power transmission start signal) and transmitsa power reception start signal when it is ready for power reception(JD2: Transmission of power reception start signal). The power feedingdevice K receives the power reception start signal from the powerreceiver J (KC3: Reception of power reception start signal) and startspower transmission (KC4: Start of power transmission). By powertransmission from the power feeding device K, the power receiver Jstarts power reception (JD3: Start of power reception).

The power feeding device K transmits a power transmission end signal tothe power receiver J by using the power transmission control function222 after transmitting a proper amount of power (KC5: Transmission ofpower transmission end signal). The power receiver J receives the powertransmission end signal from the power feeding device K (JD4: Receptionof power transmission end signal), then transmits a power reception endsignal to the power feeding device K (JD5: Transmission of powerreception end signal), and ends the power reception (JD6: End of powerreception) (D: Power reception control step). The power feeding device Kreceives the power reception end signal from the power receiver J (KC6:Reception of power reception end signal) and also ends the powertransmission (KC7: End of power transmission) (C: Power transmissioncontrol step).

Note that the start or end of power transmission from the power feedingdevice K may be at the same time as the transmission of the powertransmission start signal or the transmission of the power transmissionend signal. The start or end of power reception may also be at the sametime as the transmission of the power reception start signal or thetransmission of the power reception end signal. Since the powertransmission and the power reception occur in conjunction with eachother, the power reception by the power receiver J can be started at thesame time as the start of power transmission from the power feedingdevice K, and the power reception by the power receiver J can be endedat the same time as the end of power transmission from the power feedingdevice K. FIG. 1 illustrates an example where the power feeding device Ksignals the end of power feeding to the power receiver J and ends thepower transmission, but the power receiver J can request the end ofpower feeding of the power feeding device K to end the powertransmission from the power feeding device K.

As a result, the power load portion 150 can be operated using powerstored in the secondary battery 131 of the power storage portion 130 ofthe power receiving device portion 100. In this specification, a powerreceiver means an object which operates using received power as adriving power, and examples of the power receiver include portableelectronic devices such as mobile phones, notebook personal computers,cameras such as digital cameras or digital video cameras, digital photoframes, portable game machines, personal digital assistants, andelectronic books, transportation means driven by an electric motor usingpower (automobiles (automatic two-wheeled vehicles, three ormore-wheeled automobiles), motorized bicycles including motor-assistedbicycles, aircrafts, ships, and railroad cars), and the like.

FIG. 10 illustrates a personal digital assistant (PDA) as an example ofthe power receiver. The power receiver 10 in FIG. 10 is a personaldigital assistant including a display panel 51 in a housing 50. In thehousing 50, the power receiving device portion 100 and the power loadportion 150 are provided under the display panel 51. The power receivingdevice portion 100 includes the transmission/reception circuit portion110 which includes the antenna circuit 111, the rectifier circuit 112,the modulation circuit 113, the demodulation circuit 114, the oscillatorcircuit 115, and the like, the signal processing circuit portion 120,the memory portion 140, and the power storage portion 130 including thesecondary battery 131. An electromagnetic wave received by thetransmission/reception circuit portion 110 is stored in the secondarybattery 131 of the power storage portion 130 via the signal processingcircuit portion 120. By the supply of power stored in the secondarybattery 131 to the power load portion 150, a semiconductor integratedcircuit and the like provided in the power load portion 150 can bedriven and an image can be displayed on the display panel 51; thus, thepower receiver 10 can be operated as a personal digital assistant.

As described above, the power feeding system and the power feedingmethod in this embodiment enable a user of the power receiver to obtainmore convenience and higher added values.

It is also possible to provide a company at the power feeding end with apower feeding system and a power feeding method which can offer avariety of efficient services.

Embodiment 2

In this embodiment, another embodiment of a wireless power feedingsystem and a wireless power feeding method is described with referenceto FIG. 5 and FIG. 6.

FIG. 6 illustrates components of a power feeding device and a powerreceiver included in the wireless power feeding system of thisembodiment, in independent blocks which are classified according totheir functions. FIG. 6 illustrates an example where a detection portion(a voltage/current detection portion 160) which detects the amount ofpower stored in the secondary battery 131 of the power storage portion130 is provided in the wireless power feeding system in FIG. 2 describedin Embodiment 1. The same portions as or portions having functionssimilar to those in Embodiment 1 are similar to those in Embodiment 1and repetitive description will be omitted. In addition, detaileddescription of the same portions is not repeated.

The voltage/current detection portion 160 detects the voltage, thecurrent, or the voltage and current outputted from the secondary battery131 of the power storage portion 130 to find out the amount of powerstored in the secondary battery 131 and transmits the information to thesignal processing circuit portion 120, so that the signal processingcircuit portion 120 controls power reception.

An embodiment of a wireless power feeding method is described withreference to a flow chart of FIG. 5. Note that a power feeding device Kcorresponds to the power feeding device 20 in FIG. 6 and a powerreceiver J corresponds to the power receiver 10 in FIG. 6.

A position and resonant frequency detection step is similar to that inFIG. 1 in Embodiment 1 and is thus not described.

A power transmission control step and a power reception control step aredescribed.

The power feeding device K adjusts the frequency of a power signal to betransmitted, on the basis of the distance to the power receiver J andthe resonant frequency of the power receiver J, so as to obtain themaximum power transmission efficiency (KC1: Adjustment of powertransmission frequency). Power can be supplied to the power receiverwithout waste by transmitting a power signal to the power receiver J atan optimum frequency for high power transmission efficiency. As aresult, power feeding which is efficient and convenient for both thepower feeding device K and the power receiver J can be performed.

The power feeding device K transmits a power transmission start signalto the power receiver J (KC2: Transmission of power transmission startsignal), and the power receiver J receives the power transmission startsignal (JD1: Reception of power transmission start signal) and transmitsa power reception start signal when it is ready for power reception(JD2: Transmission of power reception start signal). The power feedingdevice K receives the power reception start signal from the powerreceiver J (KC3: Reception of power reception start signal) and startspower transmission (KC4: Start of power transmission). By powertransmission from the power feeding device K, the power receiver Jstarts power reception (JD3: Start of power reception).

In this embodiment, an example is described in which information on theamount of power stored in the secondary battery 131, which is detectedby the voltage/current detection portion 160, is also used to controlpower feeding. At the start of power reception by the power receiver J,the voltage/current detection portion 160 detects the voltage, thecurrent, or the voltage and current outputted from the secondary battery131 (JD7: Detection of voltage/current).

The voltage/current detection portion 160 finds out the amount of powerstored in the secondary battery 131 by detecting the voltage, thecurrent, or the voltage and current outputted from the secondary battery131. When the power receiver J determines that the amount of powerexceeds the capacity of the secondary battery 131, it transmits a powerreception end signal to the power feeding device K (JD5: Transmission ofpower reception end signal).

The power feeding device K receives the power reception end signal fromthe power receiver J (KC6: Reception of power reception end signal),then transmits a power transmission end signal to the power receiver J(KC5: Transmission of power transmission end signal), and ends the powertransmission (KC7: End of power transmission). The power receiver Jreceives the power transmission end signal from the power feeding deviceK (JD4: Reception of power transmission end signal) and ends the powerreception (JD6: End of power reception).

In this manner, the power receiver J can request the end of powerfeeding of the power feeding device K to end the power transmission fromthe power feeding device K.

In power feeding performed by the power feeding device and the powerreceiver, a power signal is transmitted to the power receiver at anoptimum frequency for high power transmission efficiency on the basis ofthe position and resonant frequency information of the power receiver;accordingly, power can be supplied to the power receiver without waste.

Furthermore, by finding out the amount of power stored in the secondarybattery, power transmission which is more proper to the user request canbe performed. Thus, it is possible to reduce the waste of power due toexcessive power transmission and the deterioration of the secondarybattery 131 due to the supply of power over the capacity. As a result,power feeding which is efficient and convenient for both the powerfeeding device and the power receiver can be performed.

Accordingly, it is possible to provide a power feeding system and apower feeding method which can offer a power feeding service efficientto both a user and a provider.

This embodiment can be implemented in an appropriate combination withthe configurations described in the other embodiments.

Embodiment 3

In this embodiment, another embodiment of a wireless power feedingsystem and a wireless power feeding method is described with referenceto FIG. 7 and FIGS. 8A and 8B.

In this embodiment, an example is described in which a step ofrecognizing identification information of the power receiver is addedbefore the position and resonant frequency detection step in Embodiment1 or 2. The same portions as or portions having functions similar tothose in Embodiment 1 or 2 are similar to those in Embodiment 1 or 2 andrepetitive description will be omitted. In addition, detaileddescription of the same portions is not repeated.

Identification information can be stored in the memory portion of thepower receiver. In addition, the signal processing circuit portion ofthe power feeding device has an identification function to identify theidentification information.

A wireless power feeding method of this embodiment is described withreference to a flow chart of FIG. 7. Note that a power feeding device Kcorresponds to the power feeding device 20 in FIG. 2 and FIG. 3 and apower receiver J corresponds to the power receiver 10 in FIG. 2 and FIG.3.

First, the power receiver J transmits identification information to thepower feeding device K (JA1: Transmission of identificationinformation), and the power feeding device K receives the identificationinformation of the power receiver J (KA1: Reception of identificationinformation). The power feeding device K inquires for and checks thereceived identification information (KA2: Inquiry and check ofidentification information), and identifies the power receiver J (A:Identification information recognition step). The process proceeds tothe next step, and power feeding is performed in a manner similar to thepower feeding method in FIG. 1 or FIG. 5.

The power feeding device K may store information for the identificationin the memory portion of the power feeding device K in advance.Alternatively, at the time of identification, the power feeding device Kmay communicate with another management server or the like and performidentification on the basis of information obtained from the server.Alternatively, communication between the power feeding device K and thepower receiver J may be started from the power feeding device K. Forexample, in the case where the power feeding device K have obtainedidentification information of the power receiver J, communication may bestarted by transmission of a signal for inquiring about identificationinformation to the power receiver J in order to identify (search for)the power receiver J having the identification information.

The power feeding device K can adjust the intensity of a power signal tobe transmitted, on the basis of the identification information of thepower receiver J. For example, by reading and considering the amount ofpower which can be stored in the secondary battery 131 of the powerreceiver J on the basis of the identification information, the intensityand frequency of an electromagnetic wave to be transmitted, the powertransmission time, and the like can be controlled.

Alternatively, as in FIG. 8A, the power receiver J can request the startof power feeding of the power feeding device K to start powertransmission from the power feeding device K. FIG. 8A illustrates theidentification information recognition step. First, the power receiver Jtransmits a signal for requesting power feeding to the power feedingdevice K (JA2: Transmission of power feeding request signal). The powerfeeding device K which is placed in a position where it can receive thepower feeding request signal from the power receiver J receives thepower feeding request signal (KA3: Reception of power feeding requestsignal) and transmits a signal for inquiring about identificationinformation of the power receiver J to the power receiver J in responseto the power feeding request signal (KA4: Transmission of identificationinformation inquiry signal). The power receiver J receives theidentification information inquiry signal from the power feeding deviceK (JA3: Reception of identification information inquiry signal) andtransmits identification information of the power receiver J to thepower feeding device K (JA1: Transmission of identificationinformation). The process proceeds to the next step, and power feedingis performed in a manner similar to the power feeding method in FIG. 1or FIG. 5.

The transmission of the power feeding request signal from the powerreceiver J may be controlled by a user in consideration of the amount ofpower stored in the secondary battery of the power receiver J.Alternatively, the transmission of the power feeding request signal fromthe power receiver J may be set so as to be automatically performeddepending on the amount of power stored in the secondary battery 131.

For example, as illustrated in FIG. 8B, the voltage/current detectionportion 160 detects the voltage, the current, or the voltage and currentoutputted from the secondary battery 131 (JA4: Detection ofvoltage/current), and when the power receiver J determines that theamount of power stored in the secondary battery 131 is smaller than acertain amount of power, it transmits a power feeding request signal tothe power feeding device K (JA2: Transmission of power feeding requestsignal). The process proceeds to the next step, and power feeding isperformed in a manner similar to the power feeding method in FIG. 8A andFIG. 1 or FIG. 5.

In power feeding performed by the power feeding device and the powerreceiver, a power signal is transmitted to the power receiver at anoptimum frequency for high power transmission efficiency on the basis ofthe position and resonant frequency information of the power receiver;accordingly, power can be supplied to the power receiver without waste.

Furthermore, by finding out the specific information of the powerreceiver J or the amount of power stored in the secondary battery, powertransmission which is adapted to the user request can be performed.Thus, it is possible to reduce the waste of power due to excessive powertransmission and the deterioration of the secondary battery 131 due tothe supply of power over the capacity. As a result, power feeding whichis efficient and convenient for both the power feeding device K and thepower receiver J can be performed.

In addition, it is preferable to take measures for security, such asupdating identification information including specific information likepersonal information for each power feeding, deleting unnecessaryidentification information from a power feeding device after finishing arecognition step for power feeding, or encrypting communication whentransmitting identification information.

Accordingly, it is possible to provide a power feeding system and apower feeding method which can offer a power feeding service efficientto both a user and a provider.

This embodiment can be implemented in an appropriate combination withthe configurations described in the other embodiments.

Embodiment 4

In this embodiment, another embodiment of a wireless power feedingsystem and a wireless power feeding method is described with referenceto FIG. 9.

The power feeding system and the power feeding method in thisspecification can also be applied to a plurality of power feedingdevices and a plurality of power receivers. In this embodiment, anexample is described in which the power feeding system and the powerfeeding method described in any of Embodiments 1 to 3 are applied to aplurality of power feeding devices and a plurality of power receivers.The same portions as or portions having functions similar to those inany of Embodiments 1 to 3 are similar to those in any of Embodiments 1to 3 and repetitive description will be omitted. In addition, detaileddescription of the same portions is not repeated.

For example, in the case where power is fed from one power feedingdevice to a plurality of power receivers, the position and the resonantfrequency of each of the power receivers can be found, and the frequencyof a power signal to be transmitted can be controlled so as to obtainoptimum power transmission efficiency. FIG. 9 illustrates an examplewhere power is fed to each of power receivers Ja 10 a, Jb 10 b, and Jc10 c.

The power receivers Ja 10 a, Jb 10 b, and Jc 10 c are placed atdifferent distances from a power feeding device K 20 and have specificresonant frequencies.

The power feeding device K 20 feeds power by obtaining the position andresonant frequency information of the power receivers Ja 10 a, Jb 10 b,and Jc 10 c and determining the frequencies f(d(Ja)), f(d(Jb)), andf(d(Jc)) of power signals to be transmitted, on the basis of theinformation, so as to obtain optimum power transmission efficiency foreach of the power receivers.

A power signal is transmitted to each power receiver at an optimumfrequency for high power transmission efficiency on the basis of theposition and resonant frequency information of the power receiver;accordingly, power can be supplied to the power receivers without waste.

Although FIG. 9 illustrates a case where a single power feeding deviceis used, a plurality of power feeding devices may be used. Even with aplurality of power feeding devices, power feeding between the powerfeeding devices and the power receivers can be performed by finding outinformation on the distances and resonant frequencies and optimizing thefrequencies of electrical signals to be transmitted, on the basis of theinformation, so as to obtain high transmission efficiency.

In the case where a plurality of power receivers exists within the rangein which communication with the power feeding device can be carried out,power can be transmitted only to a specific power receiver usingidentification information of the power receiver as described inEmbodiment 3.

Since identification information is found out and power feeding isperformed, a power receiver which is an intended object can be preciselymanaged, and an efficient service for a winner for a prize or the likeor a subscriber can be offered.

In addition, as described also in Embodiment 3, it is preferable to takemeasures for security, such as updating identification informationincluding specific information like personal information for each powerfeeding, deleting unnecessary identification information from a powerfeeding device after finishing a recognition step for power feeding, orencrypting communication when transmitting identification information.

This embodiment can be implemented in an appropriate combination withthe configurations described in the other embodiments.

EXPLANATION OF REFERENCE

10: power receiver, 20: power feeding device, 50: housing, 51: displaypanel, 100: power receiving device portion, 110: transmission/receptioncircuit portion, 111: antenna circuit, 112: rectifier circuit, 113:modulation circuit, 114: demodulation circuit, 115: oscillator circuit,116: power supply circuit, 117: power receiver antenna, 120: signalprocessing circuit portion, 122: power reception control function, 130:power storage portion, 131: secondary battery, 140: memory portion, 150:power load portion, 160: voltage/current detection portion, 210:transmission/reception circuit portion, 211: antenna circuit, 212:rectifier circuit, 213: modulation circuit, 214: demodulation circuit,215: oscillator circuit, 216: power supply circuit, 217: power feedingdevice antenna, 220: signal processing circuit portion, 222: powertransmission control function, 223: position and resonant frequencydetection function, 230: power supply portion, and 300: magnetic field.

This application is based on Japanese Patent Application serial no.2010-169648 filed with Japan Patent Office on Jul. 28, 2010, the entirecontents of which are hereby incorporated by reference.

The invention claimed is:
 1. A wireless power feeding system comprising:a wireless power feeding device comprising: a power feeding devicetransmission/reception circuit portion; and a signal processing circuitportion having a resonant frequency detection function and a powertransmission control function; a wireless power receiver comprising: apower receiver transmission/reception circuit portion; a signalprocessing circuit portion; and a power storage portion comprising asecondary battery, wherein the wireless power feeding device isconfigured to: receive a detection signal transmitted by the powerreceiver, the detection signal comprising a plurality of signals eachhaving a different frequency; determining a resonant frequency of thepower receiver based on the detection signal; adjust a frequency of apower signal to be transmitted by the power feeding device to the powerreceiver, based on the resonant frequency of the power receiver; andtransmit the power signal to the power receiver; and wherein thewireless power receiver is configured to: transmit the detection signalcomprising the plurality of signals each having a different frequency tothe power feeding device; receive the power signal having a frequencyadjusted to the resonant frequency of the wireless power receiver; andstore power of the power signal in the secondary battery of the powerstorage portion.
 2. A wireless power feeding system according to claim1, the wireless power receiver further comprising a voltage currentdetection portion, wherein the wireless power receiver is furtherconfigured to transmit to the power feeding device a signal forrequesting beginning or end of power feeding in accordance with adetected voltage, a detected current or detected current and voltageoutputted from the secondary battery.
 3. A wireless power feeding systemaccording to claim 1, the wireless power receiver further comprising amemory, wherein the wireless power receiver is further configured totransmit identification information stored in the memory to the powerfeeding device; and wherein the wireless power feeding device is furtherconfigured to receive the identification information.
 4. A wirelesspower feeding system according to claim 1, wherein the resonantfrequency is one of the frequencies of the plurality of signals.
 5. Awireless power feeding system according to claim 1, wherein the wirelesspower receiver is one of a portable electronic device, categorycomprising mobile phones, notebook personal computers, cameras includingdigital cameras or digital video cameras, digital photo frames, portablegame machines, personal digital assistants, and electronic books, and atransportation means driven by an electric motor, category comprisingautomobiles, motorized bicycles including motor-assisted bicycles,aircrafts, ships, and railroad cars.
 6. A wireless power feeding systemaccording to claim 1, the wireless power feeding system being configuredto perform its functions without modifying a resonant frequency of thewireless power feeding device or the resonant frequency of the wirelesspower receiver.
 7. A wireless power receiver comprising: atransmission/reception circuit portion; a signal processing circuitportion; and a power storage portion comprising a secondary battery,wherein the wireless power receiver is configured to: emit a detectionsignal apt to allow a power feeding device to detect a resonantfrequency of the power receiver, the detection signal comprising aplurality of signals each having a different frequency; receive a powersignal having a frequency adjusted to a resonant frequency of thewireless power receiver determined from the detection signal; and storepower transmitted by the power signal in the secondary battery of thepower storage portion.
 8. A wireless power receiver according to claim7, further comprising a voltage current detection portion, wherein thewireless power receiver is further configured to emit a signal forrequesting beginning or end of power feeding in accordance with adetected voltage, a detected current or detected current and voltageoutputted from the secondary battery.
 9. A wireless power receiveraccording to claim 7, further comprising a memory, wherein the wirelesspower receiver is further configured to emit identification informationstored in the memory.
 10. A wireless power receiver according to claim7, wherein the resonant frequency is one of the frequencies of theplurality of signals.
 11. A wireless power receiver according to claim7, wherein the wireless power receiver is one of a portable electronicdevice, category comprising mobile phones, notebook personal computers,cameras including digital cameras or digital video cameras, digitalphoto frames, portable game machines, personal digital assistants, andelectronic books, and a transportation means driven by an electricmotor, category comprising automobiles, motorized bicycles includingmotor-assisted bicycles, aircrafts, ships, and railroad cars.
 12. Awireless power receiver according to claim 7, the wireless powerreceiver being configured to perform its functions without modifying theresonant frequency.
 13. A wireless power feeding device comprising: atransmission/reception circuit portion; a signal processing circuitportion having a resonant frequency detection function and a powertransmission control function; and a power supply portion, wherein thewireless power feeding device is configured to: receive a detectionsignal transmitted by a power receiver, the detection signal comprisinga plurality of signals each having a different frequency; determine aresonant frequency of the power receiver based on the detection signal;adjust a frequency of a power signal to be emitted by the power feedingdevice, based on the resonant frequency; and emit the power signal. 14.A wireless power feeding device according to claim 13, wherein thewireless power feeding device is further configured to receiveidentification information emitted by the power receiver.
 15. A wirelesspower feeding device according to claim 13, wherein the resonantfrequency is one of the frequencies of the plurality of signals.
 16. Awireless power feeding method for a wireless power feeding systemcomprising the steps of: transmission of a detection signal by a powerreceiver to a power feeding device, the detection signal comprising aplurality of signals each having a different frequency; reception of thedetection signal by the power feeding device; determination of aresonant frequency of the power receiver by the power feeding device,based on the detection signal; frequency adjustment of a power signal tobe transmitted from the power feeding device to the power receiver,based on the resonant frequency; transmission of the power signal by thepower feeding device to the power receiver; reception of the powersignal by the power receiver; and storage of power transmitted by thepower signal in a power storage portion of the power receiver.
 17. Awireless power feeding method for a wireless power feeding systemaccording to claim 16, further comprising the step of: transmission ofidentification information from the power receiver to the power feedingdevice.
 18. A wireless power feeding method for a wireless power feedingsystem according to claim 16, further comprising the steps of: detectionof voltage, current, or voltage and current outputted from a secondarybattery of the power storage portion of the power receiver.
 19. Awireless power feeding method for a wireless power feeding systemaccording to claim 16, wherein the resonant frequency is one of thefrequencies of the plurality of signals.
 20. A wireless power feedingmethod for a wireless power feeding system according to claim 16, thewireless power feeding system being configured to perform its functionswithout modifying a resonant frequency of the wireless power feedingdevice or the resonant frequency of the wireless power receiver.
 21. Awireless power feeding method for a wireless power receiver comprisingthe steps of: emission of a detection signal apt to allow a powerfeeding device to detect a resonant frequency of the power receiver bythe power receiver, the detection signal comprising a plurality ofsignals each having a different frequency; reception of a power signalhaving a frequency adjusted to a resonant frequency of the powerreceiver; and storage of power transmitted by the power signal in apower storage portion of the power receiver.
 22. A wireless powerfeeding method for a wireless power receiver according to claim 21,further comprising the step of emission of identification information bythe power receiver.
 23. A wireless power feeding method for a wirelesspower receiver according to claim 21, further comprising the steps of:detection of voltage, current, or voltage and current outputted from asecondary battery of the power storage portion of the power receiver.24. A wireless power feeding method for a wireless power receiveraccording to claim 21, wherein the resonant frequency is one of thefrequencies of the plurality of signals.
 25. A wireless power feedingmethod for a wireless power receiver according to claim 21, the wirelesspower receiver being configured to perform its function withoutmodifying the resonant frequency.
 26. A wireless power feeding methodfor a wireless power feeding device comprising the steps of: receptionof a detection signal emitted by a power receiver by the power feedingdevice, the detection signal comprising a plurality of signals eachhaving a different frequency; detection of a resonant frequency by thepower feeding device, based on the detection signal; frequencyadjustment of a power signal to be emitted by the power feeding device,based on the resonant frequency; and emission of the power signal.
 27. Awireless power feeding method for a wireless power feeding deviceaccording to claim 26, further comprising the step of reception ofidentification information by the power feeding device.
 28. A wirelesspower feeding method for a wireless power feeding device according toclaim 26, wherein the resonant frequency is one of the frequencies ofthe plurality of signals.